The present invention relates to a system for producing a square wave output signal having variable phase in relation to a fixed reference signal and, more specifically, relates to a transformer coupled circuit employing logic elements for producing such variable phase square wave signals.
It is known to produce a pulse width modulated signal by varying the duration of the output voltage pulses of the two signals that are applied to an inverter circuit. Typically, in such inverter circuits silicon controlled rectifiers are employed and are triggered on for a time interval equal to a half cycle of the voltage wave.
A similar circuit is taught for varying the relative phases of two square wave signals, so that they may be used as control signals in an ampliphase kind of amplitude modulation circuit. That system is described in U.S. Pat. No. 4,319,204 assigned to the assignee hereof. Disclosed in that application is an exciter used with a pair of amplifier circuits having a common output circuit for producing the desired amplitude modulated output signal. The exciter is employed to control the relative phases of the control signals fed to the pair of amplifier circuits.
The intended result in all of such exciter systems is to produce two square wave signals which have a mutual phase relationship based upon a varying level input signal, such as an audio signal.